[R] summing columns using partial labels

[Rich FitzJohn]

Gidday,

Perhaps try something along these lines:

## Establish which 4-letter group each row belongs to
prefix <- substr(names(d), 1, 4)
gp <- match(prefix, unique(prefix))
gp[regexpr("\\.total$", names(d)) > -1] <- NA # Exclude `*.total' rows

## Sum up each of the groups
d.sums <- lapply(split(seq(along=d), gp), function(x) rowSums(d[x]))
names(d.sums) <- paste(unique(prefix), "sum", sep=".")

## Append to the end of the original data.frame
d.new <- cbind(d, d.sums)

Cheers,
Rich

On Apr 6, 2005 6:05 AM, T Petersen <Innkeyp-r at yahoo.com> wrote:
> I have a dataset of the form
> 
> Year  tosk.fai   tosk.isd   tosk.gr  .......  tosk.total       hysa.fai
> hysa.isd ...
> 
> and so on. I want to sum all the columns using the first four letters in
> the columns label(e.g. 'tosk', 'hysa' etc.). How can you do that? Also,
> the sums should be without the '.total'column (e.g. 'tosk.total') as
> this serves as a check that everything was done right.
> 
> Kind regards
> 
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-- 
Rich FitzJohn
rich.fitzjohn <at> gmail.com   |    http://homepages.paradise.net.nz/richa183
                      You are in a maze of twisty little functions, all alike